Metal injection molding is a well established process that has been used since the 1980's to create small, complex metal parts in high volumes for use in a variety of industries and applications. The metal injection molding process is typically described as a powder metallurgy process where the compaction stage is achieved through injection molding. In metal injection molding, fine metal powders are mixed with a polymeric or water based binder and this metal powder composition is injected into a mold to form a green part. The binder is a temporary vehicle for homogeneously packing the metal powder into the desired shape and holding the metal in the desired shape until the beginning of sintering. After molding, the binder is removed from the green part in a debinding process, and the brown part thus formed is sintered. FIG. 1 illustrates a typical process as is generally known in the art. Metal injection molding has proven beneficial in formation of metal parts of complex shape, particularly in high volume production processes.
Unfortunately, there are size and shape limitations in forming parts according to a metal injection molding process. These limitations are mainly imposed by the debinding and sintering processes. For instance, thick cross sections are difficult to debind and/or take too much time to debind, making this process step too cost intensive for formation of structures that include a thick cross section. In addition, unsupported areas of larger parts can deform during sintering due to the effects of gravity.
Such limitations could be overcome by joining the nascent metal injection molded part with a support substrate and thereby creating a composite. Formation of a composite could provide additional advantages as well. For instance, the amount of metal powder used could be reduced; parts that are presently difficult to make by metal injection molding due to, e.g., mold design, cost or size could be more easily fabricated; high mechanical strength or other properties could be acquired at desirable levels through combinations of different materials, for example an alloy steel feedstock powder could be combined with comparatively cheap steel support substrate; and multiple properties such as both magnetic and non-magnetic characteristics could be developed in a single composite. Such improvements could also lead to cost reductions in a formation process.
Attempts have been made to form metal injection molding composites. For instance, composites have been formed by bringing a metal powder composition and a support substrate into close contact by pressing the metal powder composition to the support substrate, for example by pressing the metal powder composition around a solid cylinder, inside a tube, or onto a flat strip. Unfortunately, the bonded joint of such composites can be weakened by the relative shrinkage of the metal powder portion in comparison with the substrate. There has also been work carried out in which green parts are bonded to one another, either by assembling previously formed green parts or by injecting multiple metal powder compositions simultaneously or successively directly onto each other. Another method of manufacturing composites involves separately metal injection molding several components of an assembly. Some of the components are then machined to exact dimensions and pre-sintered and then the composite is completed by shrink-fit or adhesive bonding of the several components to one another.
While the above describes improvement in the art, further room for improvement exists. For instance, what are needed in the art are metal injection molding composites in which a metal injection molded component is strongly adhered to a support substrate. What are also needed in the art are methods for forming metal injection molding composites that can be carried out in a high throughput system and according to an economically advantageous process.